1. Technical Field
The present invention relates to marine surveying devices, and more particularly relates to devices for locating undersea pipelines by probing of the seabed. Even more particularly, the present invention relates to a marine surveying apparatus for locating pipelines buried under the seabed using a work platform such as a barge supporting a hollow casing which can be adjustably positioned above the pipeline so that repetitive multi-position probing through the casing into the seabed can locate the pipeline by physically contacting it.
2. General Background
The field of surveying involves not only the general land surveying art but also marine surveying which is often referred to as "hydrographic" surveying. Marine surveying involves, for example, the use of depth finders, fathometers, and magnetometers in combination with positioning equipment to give a plan and/or profile position of offshore oil rigs, buried or underwater pipelines, well heads, and undersea ditches in which pipe is to be laid.
One of the problems in surveying for undersea pipelines is the problem of locating those pipelines which are buried. It is desirable to not only locate such a pipeline by plotting the plan view of the pipeline as it traverses a tract of seabed, but it is also valuable to know the pipeline profile, or the amount of soil which covers the pipeline. A lack of proper "cover" can mean an exposed pipeline which is subject to damage by dredging, anchoring, saltwater corrosion, erosion, current and the like. If the pipeline is a high pressure gas pipeline or an oil pipeline, there exists a great danger to persons and the environment if the pipeline is damaged. Buried pipelines cannot usually be accurately plotted unless physical contact with the pipeline is made. This contact is usually by means of a probe rod. A probe rod is an elongated, structural element which is usually tubular and which is thrust into the earth until the tip of the rod strikes the pipeline. If the pipe is buried very deep, the probe rod can be hollow and provided with a water jet at its tip or other such jetting means so that it will penetrate the seabed easily. Usually, the probe rod is an elongated tubular structure such as a section of one-half inch to three inch (1/2"-3") pipe having a hollow bore. Water for jetting can be supplied to the probe rod by a hose connection to a water pump. In an offshore environment, probe rods can be very long and can be difficult to support and handle. For example, if a pipeline is located in twenty-five feet of water and buried under the seabed an additional five feet, the pipeline lies thirty feet beneath the water surface. In order to reach the pipeline and have some of the probe rod exposed so that workers on a barge or boat can handle it, a probe rod would be preferably thirty-five to forty feet in length to locate such a pipeline located thirty feet below water surface.
The problem of support of a probe rod by workers on a boat can be unexpectedly compounded by wave action which acts upon the hull of the vessel occupied by the surveyors. The probe rod is preferably supported in a vertical direction so that a surveying instrument such as a transit, or theodalite can sight the top of the probe rod in order to determine position of the pipeline. A problem exists in that long probe rods are very difficult to vertically orient for surveyors standing on the deck of a work platform such as a boat or a barge. Thus, the elongated probe rods become a source of error for the survey if they are not supported in a vertical fashion. Another problem is the weight of the probe rod itself. Probe rods of, for example, forty feet in length when filled with water and when attached to jetting hoses and the like can become very heavy requiring a number of workers to both support the pipe and to properly align it so that each penetration of the seabed can be made in order to search for the pipeline. This cumbersome process becomes quite expensive and time-consuming when the exact position of the pipeline is not known and the probe rod must be thrust into the seabed over and over until the tip of the probe rod strikes the pipeline.